Voice disorders are among the most prevalent disorders affecting people with communication disabilities. People afflicted with these disorders have difficulty communicating with others, the disorders may adversely affect their careers, and the people often become socially isolated. There is little we can do to prevent these disorders without a solid understanding of their cause. Part of the reason for this lack of understanding is because of the lack of basic knowledge of normal control mechanisms of the voice. It is assumed that sensory feedback may be involved in control of the voice, but there is little hard evidence to support this claim. The overall goal of this research project is to understand the function of sensory feedback in the control of voice fundamental frequency (F0) and intensity. People use their voice for a variety of functions such as speech, singing and emotional expression. To fully understand how voice F0 and intensity are controlled, we must study them in different tasks, because it is known from research in other motor systems that the importance of sensory feedback varies according to the demands of the task. Auditory and kinesthetic feedback from the larynx will be studied as subjects are engaged in different vocal tasks. The overall hypothesis of the proposal is that the magnitude of pitch and loudness shift reflexes depend on the presence of laryngeal kinesthetic feedback and vary according to the importance of sensory feedback for accuracy of F0 and intensity control in specific tasks. By testing vocal reflexes as people are using their voice in different tasks, we will learn how sensory feedback is modulated in the tasks. It is hypothesized that auditory reflex magnitudes will increase in tasks that require skilled use of the voice, both in frequency and intensity of phonation. The tasks to be tested include pitch matching, loudness regulation, speech and singing a musical scale. It is also hypothesized that kinesthetic and auditory feedback interact in their control of the voice. This interaction was shown in pilot studies in which the pitch-shift reflex dramatically increased in magnitude when the vocal folds were anesthetized or when vibratory stimuli were applied to the larynx. Altering kinesthetic feedback from the vocal folds and simultaneously testing auditory reflexes will provide important information on brain mechanisms that govern interaction between these two sources of feedback.